Refractory metal alloys and method of making same



Patented May '31, 1938 UNITED STATES REFRACTORY METAL ALLOYS AND METH- 01) OF MAKING SAME William J. Beer, Union, N. L, assignor to Sirian Wire and Contact Company, Newark, N. 1., a corporation of Delaware No Drawings 19 Claims.

The present invention relates to the production of hard metal alloys, and it particularly relates to the productionof alloys which may be utilized for making cutting tools, wear-resisting implements of various types, and so forth.

It has been proposed to make hard metals from combinations of tungsten carbide and cobalt which are sintered together at temperatures between 1500 C. and 1600' C. It has been found, however, that these metals are not altogether satisfactory in their hardness and wearing qualities, and involve certain difiiculties in the process of manufacture.

It is among the objects of the present invention to prepare an improved, hard metal alloy at low cost and of high quality in respect to strength, hardness and density, which may be made of uniform quality from batch to batch, and which will have a sumcient degree of toughness and density to enable its wide utilization in connection with wear-resisting bodies, cutting tools, working implements, and so forth.

Other objects will be obvious and will appear on consideration of the following specification.

In accomplishing the objects of the present invention it has been found most suitable to prepare a finely divided refractory metal, such as tungsten, by reduction from a tungsten compound such as tungstic oxide or tungstic acid in a hydrogen atmosphere. This finely divided tungsten, which may be first milled and/or sifted through a 180 mesh or 200 mesh screen, is then compounded with an additional metal compound such as a compound, and preferably an organic compound, of cobalt, nickel or iron. The combined mixture is then reduced, preferably in an electric furnace and in a hydrogen and/or hydrocarbon atmosphere between 1000 C. and 1350 C., and after reduction is mixed with carbon and again heated in a reducing atmosphere to form the desired carbide or carbides. Finally, the carbides are powdered and formed into shapes. These shapes are sintered at a temperature of between 1400" C. and 1600 C. for several hours.

In carburizing and sintering, it has been found desirable to maintain a hydrocarbon atmosphere or an atmosphere containing hydrogen and some hydrocarbon, since this appears to prevent loss of carbon from the carbides, as sometimes occurs when a stream of hydrogen is continuously passed over the carbonaceous mixture. The same effect may also be obtained in some cases by providing a stagnant hydrogen body, as in a plugged carbon tube, thus preventing flow of hydrogen across the material being carburized or sintered. V

The prefered hydrocarbons are those of a non-saturated nature, such as acetylene, methyl acetylene, ethylene, benzene, toluene, xylene, propylene, butylene, allylene, and so forth.

It has been found most satisfactory to use Application July 29, 1936, erlal No. 93,171

an organic acid salt of cobalt, nickel or iron, such as the cobalt or nickel salts of acetic, formic, oxalic, tartaric, citric, benzoic and other organic acids. With these cobalt or nickel salts, both beheated with the finely divided, pure refractory metal in a reducing atmosphere at a temperature of 400 C. to 800 C. for a period of two to six hours, that a mixture of a refractory metal and additional metal particularly adapted to be converted into the hard metal alloy by carburization is formed.

Instead of, or in combination with, the finely divided metallic tungsten, finely divided refractory metals such as tantalum, titanium, chromium, molybdenum, uranium, vanadium, thorium, and so forth, may be employed, such metals preferably not being utilized in greater proportion than the tungsten. Tantalum is the preferred additional refractory metal.

Where mixtures of refractory metals are to be employed a pulverized or milled mixture of the metals may contain, for example, between 1% and 10% of titanium, vanadium, and/or chromium, from 60% to 75% of tungsten, and from 10% to 25% of tantalum. Where chromium is also included, it may replace the titanium or.

vanadium, or it may be utilized in the amoun of between 1% and 5%.

It has been found most desirable to combine tungsten and/or other refractory metals in finely divided form with substantial amounts of cobalt or nickel, by adding liquid dispersions of the organic cobalt or nickel compounds to the oxides or hydroxides of the refractory metals, or more preferably, by mixing aqueous solutions of cobalt or nickel acetate with the finely divided reduced metallic tungsten or other refractory metal. The finely divided refractory metal may be added to or sprinkled into a solution, slurry or liquid dispersion of the organic cobalt or nickel compound. In lieu of part or all of the cobalt acetate it is possible to use other soluble salts, such as cobalt lactate or cobalt glycerate, and preferably the cobalt salt is used in the form of a concentrated water solution which may be, saturated and even carry suspended particles of the cobalt salt.

It is also possible to use slurries of insoluble cobalt compounds, such as cobalt stearate or oxalate. In lieu of these cobalt compounds it is possible to include the corresponding iron or nickel compounds.

The proportioning of the refractory metal, or of the additional metal such as cobalt, nickel or iron, or of the carbon, is preferably such that .zmices, between about 88% and 90% and 36.1% cobaltous acetate.

the final refractory metal will constitute between 50% and 80% of the alloy, or in some inof the alloy; while the cobalt or nickel will constitute between about 10% and 11% of the alloy, or in some instances, more than 25% of the alloy; and the carbon will constitute up to 2% to 3% of the alloy, and even up to between 10% and 15% in certain instances.

It has been found suitable in certain instances to use the following percentages of elements and compounds to make up the hard alloy: 60% tungsten metal powder, 3.9% powdered carbon The relation between the amounts of tungsten and carbon generally may remain as indicated above, but the percentage of cobaltous acetate may be varied. That is, if the percentage of cobaltous acetate is 30, then the combined percentages of tungsten and carbon will be '70, but the ratio of the two should be as 60 is to 3.9.

A mixture of tungsten and cobaltous acetate may be made first and reduced in a hydrogen atmosphere at 600 C. for four hours. This product may then be ground and mixed with the powdered carbon. This mixture may then be loaded in carbon tubes and heated in an electric furnace at a temperature of about 1400" C. for one hour. The carbonized material may then be pressed into the desired shapes and sintered in a carbon tube in an electric furnace at 1500 C. for one-half hour.

If desired, before incorporation of the tungsten or'other refractory metal with the cobalt, nickel or iron salt, it may be ground, milled or mixed with finely divided pure carbon, but most desirably carbon is not incorporated into the mixture until after reduction of the mixture of the tungsten and cobalt compound to metallic form.

By way of another example: 340 grams of crystals of chemically pure cobalt acetate are pulverized and dissolved in a liter of water with vigorous shaking. This solution is then poured into an evaporating dish and heated. 660 grams of pure tungsten metal powder, which has been produced by reduction of tungstic oxide or acid in a reducing atmosphere and which has been previously bolted through a 180 mesh sieve, are then sprinkled into the solution in small quantitles at a time. This mixture is then evaporated to dryness with constant stirring, which will take approximately ten hours. The residue is powdered and the powder is then bolted through a 180 mesh sieve. The mixture is then reduced in a hydrogen atmosphere to form a mixture of metallic cobalt and tungsten, which mixture is powdered and again bolted and mixed with finely divided sugar carbon.

This powdered mixture is then loaded into carbon tubes and heated in a molybdenum-wound hydrogen atmosphere furnace for five hours at 1200" C. to 1350 C. The hydrogen gas, before entering the furnace, is bubbled through benzol (C6H6) at room temperature. The fiow of gas is maintained approximately at ten cubic feet per hour. If acetylene is used, it is added to the hydrogen gas in the ratio of one part acetylene (C2H2) to two parts hydrogen. The tubes are then pushed into the cooler and removed when cold. The resultant mixture is crushed in a mortar and milled for approximately one week. It is then bolted through a 180 mesh sieve and the resultant fine powder formed under pressure of approximately twenty ton per square inch to the desired shape. The formed pieces are .salts, followed by reduction to then placed in carbon tubes and heated in a molybdenum-wound hydrogen or hydrocarbon atmosphere furnace to about 1450 C. to 1550 C. for thirty minutes or longer, dependent upon the size of the pieces. The tubes are then pushed into the cooler and when cold withdrawn.

If it is not desired to use a hydrocarbon atmosphere during sintering or carburizing, a substantially stagnant hydrogen atmosphere may be employed. By heating the cobalt-tungsten-carbon mixture or the cobalt tungsten carbide in a hydrogen stream, some of the carbon was found to be removed from the mixture or the carbide by being taken up by the hydrogen and passing out as a hydrocarbon. When the carbide was loaded in a carbon tube, plugged at each end with carbon plugs, one of which contained a small vent hole, and this carbon tube was placed in a hydrogen atmosphere, it was carbide was not affected by the hydrogen, nor was any carbon removed. This procedure may be applied both to the sintering of the pressed found that the parts and to the heating of a mixture of mate- :ilals used to form the carbide during carburiza- The present application is particularly directed to the combination of mixtures of refractory metals themselves with cobalt or nickel organic metal, carburization, forming and sintering. The processes of combining refractory metal carbides with a liquid dispersion or solution of cobalt acetate or other cobalt or nickel salts and making said alloys from mixtures of refractory metal carbides are more fully described and claimed in co-pending applications Serial No, 93,733, filed July 31, 1936, and Serial No. 93,734, filed July 31, 1936.

Many other changes could be effected in the particular features of process treatment disclosed, and in specific details thereof, without substantially departing from the invention intended to be defined in the claims, the specific description herein merely serving to illustrate certain elements by which, in one embodiment, the spirit of the invention may be effectuated.

What I desire to claim is:

1. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises forming an intermediate combination of an organic acid salt selected from the group consisting of the organic salts of iron, cobalt and nickel and the finely divided refractory metal by evaporating a solution of the organic acid salt containing the refractory metal to dryness, then heating the combination in a reducing atmosphere, and then carburizing.

2. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises forming an intermediate combination of a finely divided refractory metal, carbon and an organic acid salt of cobalt by evaporating a solution of the organic acid salt containing the metal and carbon to dryness, and then heating the combination in an atmosphere containing a hydrocarbon.

3. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises forming an intermediate combination of a cobalt organic acid salt and the finely divided refractory metal by evaporating a solution of the cobalt salt containing the refractory metal to dryness, and then carburizing the combination by heating it with carbon in an atmosphere consistingof hydrogen and a hydrocarbon.

4. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises providing a finely divided refractory metal powder by reduction of the metal oxidein hydrogen, mixing the metal with a concentrated aqueous solution of a cobalt organic salt, reducing to .dryness by evaporation, mixing with carbon, and heating in a reducing atmosphere to form the hard metal alloy.

5. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises providing a finely divided refractory metal powder by reduction of the metal oxide in hydrogen, mixing the metal with a concentrated aqueous solution of an organic acid salt of a metal selected from the group consisting of iron, nickel and cobalt, reducing, mixing with carbon, and heating in a reducing atmosphere to form the hard metal alloy.

6. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises providing a finely divided refractory metal powder by reduction of the metal oxide in hydrogen, mixing the metal with a solution of an acetate of a metal selected from the group consisting of iron, nickel and cobalt, evaporating the mixture to dryness, reducing, carburizing, and heating in a reducing atmosphere to form the hard metal alloy.

7. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises providing a finely divided refractory metal powder by reduction of the metal oxide in hydrogen, mixing the metal with a solution of an acetate of a metal selected from the group consisting of iron, nickel and cobalt, evaporating the mixture to dryness, reducing, carburizing, and heating in a. hydrocarbon containing reducing atmcsphere to form the hard metal alloy.

8. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises'providing a finely divided refractory metal powder by reduction of the metal oxide in hydrogen, mixing the metal with carbon and a concentrated aqueous solution of an organic salt of a metal selected from the group consisting of iron, nickel and cobalt, evaporating to dryness and heating the dry residue from evaporation in a reducing atmosphere to form the hard metal alloy.

9. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises providing a finely divided refractory metal powder by reduction of the metal oxide in hydrogen, mixing the metal with a solution of cobalt acetate and carbon, evaporating to dryness and heating in a hydrocarbon containing 1reducing atmosphere to form the hard metal al- 10. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises heating together a mixture of the refractory metal, carbon, and cobalt acetate, resulting from the evaporation to dryness of a solution of cobalt acetate containing the refractory metal and carbon, in ahydrocarbon containing reducing atmosphere. v

11. A method of making a hard metal alloy containing a refractory metal and carbon, which comprises adding the finely divided refractory metal to a cobalt acetate solution, evaporating to dryness, pulverizing, mixing with carbon, re-

ducing in a hydrogen-hydrocarbon atmosphere, forming, and then sintering in an atmosphere of the same composition.

12. A hard metal alloy formed of a reduction product of a mixture of a refractory metal, carbon, and an organic salt of a metal selected from the group consisting of iron, cobalt and nickel, the refractory metal particles being each encased in and cemented together by coatings of said last mentioned metal, said alloy being formed by mixing the metal and the carbon with a concentrated solution of the organic salt, evaporating to dryness with agitation, pulverizing, reducing the pulverized mixture in hydrogen, forming and sintering.

13. A hard metal alloy formed of a reduction product of a mixture of a refractory metal, carbon, and cobalt acetate, the refractory metal particles being each encased in cobalt, said alloy being formed by mixing the metal and the carbon in finely divided form with a concentrated solution of cobalt acetate, followed by evaporation to dryness with agitation, pulverizing, re-

duction of the pulverized material in hydrogen, forming and sintering.

14. A hard metal alloy formed of a reduction product of finely divided tungsten, carbon, and cobalt acetate, the tungsten particles being each encased in cobalt, said alloy being formed by mixing the finely divided tungsten and carbon with a concentrated cobalt acetate solution, followed by evaporation to dryness with agitation. pulverizing, reducing the pulverized material in hydrogen, forming and sintering.

15. A process of forming tungsten-cobalt carbides which comprisesadding finely divided tungsten to a cobalt acetate solution, evaporating to dryness, pulverizing, mixing with carbon, reducing in a hydrocarbon containing reducing atmosphere, forming and then sintering.

16. A process of forming tungsten-cobalt car-- bides which comprises milling finely divided tungsten coated with finely divided cobalt acetate and with finely divided carbon, said coating being obtained by evaporating to dryness a solution of cobalt acetate containing finely divided tunsten, 9.11116. heating the mixture in a reducing atmosp ere.

17. A process of forming tungsten-cobalt car bides which comprises mixing finely divided tungsten' coated with cobalt acetate, said coating being obtained by evaporating to dryness a solution of cobalt acetate containing finely divided tungsten, heating in a reducing atmosphere, mixing with carbon, and again heating the mixture in a reducing atmosphere. a

18. A process of forming tungsten-cobalt carbides which comprises mixing finely divided tungsten, tantalum, carbon and a concentrated aqueous solution of an organic acid salt of cobalt, evaporating to dryness to form a dry residue and then heating the residue in a reducing atmosphere.

19. A process of forming tungsten-cobalt carbides which comprises mixing finely divided tungsten coated with cobalt acetate and carbon, said coating being obtained by evaporating to dryness a solution of cobalt acetate containing finely divided tungsten, and then heating the mixture in a reducing atmosphere.

WILLIAM J. BEER. 

